Neonatal sepsis is a devastating illness with of mortality of 50% or greater, and current therapeutic modalities provide no effective means of salvaging a greater percentage of this population. We have recently described a new finding in animal and human neonatal sepsis, that of exhaustion of the supply of neutrophils normally held in reserve for periods of increased need. We suggest that the presence of neutrophil supply exhaustion signals a poor outcome in neonatal sepsis, and also represents an important physiologic factor in the demise of nonsurvivors. We plan to explore this possibility by studying the blood and marrow neutrophil changes in human and neonatal dog infection, and to attempt to salvage subjects with inadequate neutrophil supply by neutrophil transfusion therapy. The mechanism of neutrophil supply exhaustion will be studied in kinetic experiments.